The Brontosaurus, whose name means "thunder lizard" in Greek, is one of the most famous dinosaurs of all. However, between 1903 and 2015, scientists were convinced Brontosaurus and Apatosaurus were the same thing!

A long time ago Dr. O. C. Marsh discovered a small four legged dinosaur with a long neck. He decided to name the dinosaur Apatosaurus meaning deceptive lizard. Later the same scientist discovered a much bigger dinosaur of the same type. Because the back bones seemed different he decided it was a different dinosaur. This dinosaur was so big he decided to name it Brontosaurus. When scientists looked at these fossils later they realized that the Apatosaurus was the same animal as the Brontosaurus. Scientists use the first name given to an animal, so they decided to rename the Brontosaurus to Apatosaurus because Apatosaurus came first. Scientists now know that the back bones of the Apatosaurus grew together as the animal gets bigger. It was because the back bones changed that Dr. Marsh thought they were different animals.

Dr. Marsh also made the Brontosaurus very popular. He put the first full dinosaur skeleton on display in a museum for everyone to see. The bones he put on display where his Brontosaurus bones, and Brontosaurus became very popular. Dr. Marsh made some other mistakes about the Brontosaurus. When he put the Brontosaurus skeleton together some bones were missing, even the skull. He used bones from other dinosaur digs that he thought belonged to Brontosaurus. He accidentally put a head from a dinosaur called the Camarasaurus onto the body of an Apatosaurus. He also thought the Brontosaurus had lived mostly in the water. This was another mistake! The rocks that scientists find Apatosaurus bones in do not come from swampy areas.

It took almost 100 years after Brontosaurus was first named for two scientists, Jack McIntosh and David Bermanbase, to find these mistakes, and put the right head on the right body at last!

But then, in 2015, a group of scientists examined the neck structure of the Brontosaurus skeletons, and discovered Brontosaurus was a separate kind of dinosaur after all!

Of course, the right head for the Brontosaurus was eventually found...and now Apatosaurus and Brontosaurus are separate once more.